The present invention relates to an electrical resistance heating element for an electric furnace, as well as to a process for manufacturing such a resistance element.
Electrical resistance heating elements are produced, for example, by sintering ceramic particles, and particularly silicon carbide particles.
Silicon carbide, which is used widely for the manufacture of such heating elements, allows relatively robust resistance elements having excellent thermal properties to be obtained.
Nevertheless, such resistance elements have drawbacks in the case of their use at high temperature and in an oxidizing atmosphere, insofar as the silicon carbide particles are able to oxidize relatively rapidly in the presence of oxygen.
Such oxidation is accompanied by a not insignificant change in the value of the resistivity, this having to be compensated for by increasing their supply voltage.
The rapid oxidation of current silicon carbide resistance elements is firstly due to their considerable porosity, which facilitates the reaction between oxygen and silicon carbide.
The premature ageing of such resistance elements is also due to the nature of the components added to the silicon carbide which produce, at high temperature, a low-viscosity secondary phase. The oxygen can then easily diffuse into the core of the material and oxidize the heating element.